Split Screen


I’ve no idea when it happened, it was after one of the updates, perhaps to iOS11, but split screen no longer works on my iPad Air 2.
Was it removed for older iPads at some point? I didnt alter any settings so it ought to work. Suggestions for finding a solution?

[edit] ARGHHHH I should search before asking here. So, for those who also have the issue, theres a site which explains the changes.